culori

Culori is a comprehensive color library for JavaScript designed for working across many color spaces. It provides support for color spaces defined in the CSS Color Module Level 4 specification. Key features include:

• Color conversion
• Color interpolation
• Color difference formulas
• Blending functions

Culori distinguishes between color models and color spaces:

• Color Model: A method of describing colors along specific dimensions (e.g., RGB describes color as a combination of red, green, and blue).
• Color Space: A color model combined with a precise description of how those colors are interpreted (e.g., sRGB, Display P3, and ProPhoto RGB all use the RGB model but define different primary colors and color ranges).

All color spaces in Culori support an optional alpha channel with a range of [0, 1].

Fixup methods adjust channel values before interpolation to ensure better visual results for circular or special channels.

Hue Fixup

Used for circular hue channels.

• fixupHueShorter(values): (Default) Interpolates along the shortest path around the hue circle.
• fixupHueLonger(values): Interpolates along the longest path.
• fixupHueIncreasing(values): Ensures every hue is larger than the previous.
• fixupHueDecreasing(values): Ensures every hue is smaller than the previous.
• To treat hues as normal numbers, override the fixup with an identity function: h: { fixup: arr => arr }.

Alpha Fixup

• fixupAlpha(values): (Default) Converts all undefined values to 1 (full opacity), unless all values are undefined.

Culori does not use a Color class. Instead, colors are represented as plain JavaScript objects. Every color object must include a mode property that identifies its color space. It may optionally include an alpha property for transparency. The specific channel names (e.g., r, g, b, h, s, l) and their expected ranges depend on the mode used.

/* A RGB color */
{
  mode: 'rgb',
  r: 0.1,
  g: 0.2,
  b: 1,
  alpha: 1
}

The XYB color model is part of the JPEG XL Image Coding System. It is an LMS-based model that facilitates perceptually uniform quantization.

XYB is defined in relationship to sRGB and has a default 'Chroma from Luma' adjustment applied so that colors with { x: 0, b: 0 } are achromatic. It does not have gamut limits.

Culori distinguishes between implicit and explicit opacity. An undefined value on the alpha channel does not necessarily mean the color is opaque; rather, it indicates that the opacity is unknown or not specified.

For example, the hex string #ff0000 has an implicit alpha, whereas #ff0000ff has an explicit alpha. This allows developers to decide how to interpret undefined alpha values during color processing.

Cubehelix is a color scheme described by Dave Green and expanded into a cylindrical color space.

Serialized as color(--cubehelix h s l). Cubehelix does not have gamut limits.

ICtCp (or ITP) is a color space developed by Dolby Laboratories and included in the CSS HDR Color Module Level 1 specification.

Serialized as color(--ictcp i t p). ICtCp is the basis of the $\Delta E_{ITP}$ color difference metric. It does not have gamut limits.

Jzazbz is a perceptually uniform color space for high dynamic range and wide gamut signals.

jab (Cartesian)

jch (Cylindrical)

Jzazbz spaces do not have gamut limits.